_title: Display Logic and Input

_section: Display Logic and Input

When creating an Application, it is useful to convert between
user-friendly strings (usually displaying **ether**) and the
machine-readable values that contracts and maths depend on
(usually in **wei**).

For example, a Wallet may specify the balance in ether, and
gas prices in gwei for the User Interface, but when sending
a transaction, both must be specified in wei.

The [parseUnits](unit-conversion) will parse a string representing
ether, such as ``1.1`` into a [BigNumber](bignumber) in wei, and is
useful when a user types in a value, such as sending 1.1 ether.

The [formatUnits](unit-conversion) will format a [BigNumberish](bignumberish)
into a string, which is useful when displaying a balance.


_subsection: Units

_heading: Decimal Count

The //unit// specified may be an integer, which indicates how
many decimal place the unit has. For example, 1 ether has 18 decimal
places for wei, and if this library were used with Bitcoin, 1 BTC
has 8 decimal places for satoshis.

_heading: Named Units

In addition to specifying //unit// as a number of decimals, there
are several common units, which can be passed in as a string:

- **wei** --- 0
- **kwei** --- 3
- **mwei** --- 6
- **gwei** --- 9
- **szabo** --- 12
- **finney** --- 15
- **ether** --- 18


_subsection: Functions

_heading: Formatting

_property: utils.commify(value) => string
Returns a string with value grouped by 3 digits, separated by ``,``.


_heading: Conversion @<unit-conversion>

_property: utils.formatUnits(value [ , unit = "ether" ] ) => string
Returns a string representation of //value// formatted with //unit//
digits (if it is a number) or to the unit specified (if a string).

_property: utils.formatEther(value) => string
The equivalent to calling ``formatUnits(value, "ether")``.

_property: utils.parseUnits(value [ , unit = "ether" ] ) => [BigNumber](bignumber)
Returns a [BigNumber](bignumber) representation of //value//, parsed with
//unit// digits (if it is a number) or from the unit specified (if
a string).

_property: utils.parseEther(value) => [BigNumber](bignumber)
The equivalent to calling ``parseUnits(value, "ether")``.